1. Field of the Invention
The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device used as a light source for an optical communication system.
2. Description of the Prior Art
In the optical communication technology which uses optical fiber as a transmission medium, a light source capable of emitting infrared light beams in the band of 1300 nm or 1500 nm is used because, due to the physical properties of the optical fiber material, less loss is produced for the light beams in this infrared range during their transmission through the optical fiber. Conventionally, a semiconductor laser device as schematically shown in FIG. 6 has been used as a light source emitting infrared light beams in the above range. Such a semiconductor laser device comprises an infrared semiconductor laser chip 101 mounted on a package stem 103 with a heat sink 102 therebetween. These components are covered airtight with a cap provided with a glass window 105. Infrared laser beams 104 generated from the laser chip 101 are emitted outside through the glass window 105 with a spread of a predetermined angle.
The above conventional semiconductor laser device is disadvantageous in that the emitted laser beams having a peak wavelength of 1300 nm or more in the infrared range are not visible and therefore can not be visually located. In such a semiconductor laser device, an additional provision of a device for converting the emitted infrared laser beams 104 to visible light beams is required when the laser beams 104 are coupled to an optical fiber or introduced to a certain optical component, which results in inefficient operation. Further, since the laser beams 104 are not visible, the operator might look straight at the laser beams 104 without being aware of it, which may cause loss of eyesight if the laser chip 101 has a high power.
The objective of the present invention is to provide a semiconductor laser device in which laser beams emitted therefrom can be visually located, thereby securing improved efficiency and safety in the operation.